Compressor oil pressure control method and unit

ABSTRACT

The present invention relates to the art of refrigeration and more particularly to a method of regulating the cooling process by controlling the oil pressure in a compressor. The system prevents the accumulation of the liquid refrigerant in the crankcase of the compressor. The system allows a compressor to continue to work without interruption.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to refrigeration systems ingeneral, and more specifically to a method for controlling compressoroil pressure in these systems using different refrigerants that dissolvethe lubricant.

[0003] 2. Background of the Prior Art

[0004] Oil is usually used to lubricate refrigeration compressors. Theoil pressure of a compressor must be sufficient to support the minimalnecessary amount of oil lubricant. If the oil pressure falls below apressure necessary to support that minimal required amount of lubricant,the compressor can be damaged. That is why refrigeration systems have aspecial device to turn the compressor off when the pressure of the oilin the system reaches the minimum level. The oil from the compressor isevacuated with the refrigerant vapor. After the evaporation of theliquid refiigerant has taken place in the evaporator of therefrigeration system, the oil returns to the compressor either byrefrigerant vapors or separately from the refiigerant.

[0005] In U.S. Pat. No. 3,978,685 by M. Taylor, issued Jul. 14, 1975,the oil returns to the compressor with the refrigerant vapors from theevaporator. In this case a certain amount of liquid refrigerant canenter the compressor along with the oil. This cannot be evaporated bythe same method as in the evaporator. The oil pressure drops and ablocking device turns the compressor off. A certain amount of time andspecial preparations are required to restart the compressor again.

[0006] A similar situation is described in U.S. Pat. No. 4,631,926 byGoldstein, et. al., issued on Dec. 30, 1986, which states that when theoil carrying liquid refrigerant separates from the vapor, therefrigerant moves to the compressor through a special thermal exchangeheater. A significant amount of the refrigerant returns with the oil tothe compressor due to the existing inertia of the system, which supportsa temperature level of the mixture of the oil and the refrigerant. Itleads to the same disadvantages of the system as in U.S. Pat. No.3,978,685.

SUMMARY OF THE INVENTION

[0007] The present invention relates to a method of controlling the oilpressure in a compressor in order to allow it to work withoutinterruption. This can be accomplished by the use of the followingmethod. Practice shows that the oil pressure changes stepwise when theliquid refrigerant is accessing into the compressor. At the beginning,the pressure does not drop significantly and stays higher then theallowed minimum. As the liquid refrigerant continues to enter thecompressor, the oil pressure drops significantly and reaches acritically low level. When the oil along with the liquid refrigerant isprevented from entering the compressor immediately after the first dropof pressure, the oil pressure will be elevated. The elevation inpressure is due to the extraction of the excess amount of liquidrefrigerant from the oil in the compressor. Thereafter, the compressorcan continue to work without interruption.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0008]FIG. 1 illustrates a schematic representation of the unit in whichoil together with the liquid refrigerant is returned to the compressor.

[0009]FIG. 2 illustrates a schematic representation of an alternativeembodiment of the unit where oil is returned to the compressor togetherwith refrigerant vapor.

[0010]FIG. 3 illustrates a schematic representation of an alternativeembodiment of the unit where oil is returned to the compressor togetherwith refrigerant vapor, with a controller placed on the line connectedto a condenser and an evaporator.

DETAILED DESCRIPTION

[0011] Referring to FIG. 1, there is generally shown a unit consistingof a connected series of a compressor 1, a condenser 2, an evaporator 3,a suction accumulator 7 with inlet 5 connected to said evaporator 3 byline 4, and two outlets 6 and 9. Outlet 6 is connected to saidcompressor 1 by suction line 8 and outlet 9 is connected to saidcompressor 1 by return line 10. On said return line 10 a device 11 isinstalled to adjust an oil refrigerant liquid mixture. Said device 11 isconnected electrically by line 12 to a regulator 13 with a set pointadjuster 14 and to, said compressor 1 by line 15.

[0012] Refrigerant vapor compressed in the compressor 1 enters thecondenser 2 where it becomes a liquid and enters the evaporator 3 whereit is boiled. The refrigerant vapor containing oil enters the suctionaccumulator 7 through line 4 and then through inlet 5. The mixture isseparated in said suction accumulator 7 into a vapor and a liquid partcontaining mainly oil and some liquid refrigerant. The mixturecontaining oil and liquid refrigerant is drawn to the compressor 1 fromthe suction accumulator 7 through outlet 9 by return line 10. When theinitial part of this mixture, containing an excess of liquid refrigerantenters the compressor 1 the oil pressure immediately reduces to a levelthat is still above the minimal level allowed for the compressor 1 towork safely. Regulator 13 monitors the oil pressure value of thecompressor 1 and compares this pressure value to that installed on theset-point adjuster 14. When this first reduction of oil pressure occurs,the controller 11 closes the line 10 and prevents the entrance of liquidoil-refrigerant mixture into the compressor 1. In a short period of timeliquid refrigerant enters the compressor 1 and evaporates, the oilpressure increases, the regulator 13 opens the controller 11, and theoil continues to return to the compressor 1. This system provides anuninterrupted safe operation of the compressor.

[0013] In referring to FIG. 2, there is a unit consisting of a connectedseries of a compressor 1, a condenser 2, and an evaporator 3, which isconnected to said compressor 1 by suction line 16. A controller 11 isinstalled on said suction line 16 to adjust the oil-refrigerant liquidmixture. Said controller 111 has an electrical connection by line 12 toa regulator 13 with a set-point adjuster 14 and a connection to saidcompressor 1 by line 15.

[0014] Refrigerant vapor become compressed in the compressor 1 andenters the condenser 2 where it becomes a liquid and enters theevaporator 3 where it is boiled. The refrigerant vapor containing oil isdrawn to the compressor 1 by suction line 16. When the first part ofthis mixture, containing an excess of liquid refrigerant, enters thecompressor 1 the oil pressure immediately reduces to a level, which isstill above the minimal level allowed for the compressor 1 to worksafely. The regulator 13 monitors the oil pressure value of thecompressor 1, comparing this pressure value to the one established onthe set-point adjuster 14. Controller 11 closes the line 16 when thetarget pressure is reached. This prevents the entrance of liquidoil-refrigerant mixture into the compressor 1. In a short period of timeliquid refrigerant enters the compressor 1 and evaporates, the oilpressure increases, the regulator 13 opens the controller 11, and theoil continues to return to the compressor 1. This system provides anuninterrupted safe operation of the compressor.

[0015]FIG. 3 depicts a unit consisting of a connected series of acompressor 1, a condenser 2 connected to an evaporator 3 by line 17,respectively, and the evaporator 3 connected to said compressor 1 bysuction line 16. A controller 11 is installed on said line 17 to adjustthe oil-refrigerant liquid mixture. Said controller 11 has an electricalconnection by line 12 to a regulator 13 with a set-point adjuster 14 andto said compressor 1 by line 15.

[0016] Refrigerant vapor compresses in the compressor 1 and enters thecondenser 2 where it becomes a liquid and enters the evaporator 3 whereit is boiled. The refrigerant vapor containing oil is drawn to thecompressor 1 by suction line 16. When the first part of this mixture,containing an excess of liquid refrigerant, enters the compressor 1 theoil pressure immediately decreases to a level, which is still above theminimal level allowed for the compressor 1 to work safely. The regulator13 monitors the oil pressure value of the compressor 1, comparing thispressure value to the one installed on the set-point adjuster 14, andcloses the line 17 by means of controller 11. Controller 11 closes theline 16 when the target pressure is reached. This prevents the entranceof liquid oil-refrigerant mixture into the compressor 1. In a shortperiod of time liquid refrigerant enters the compressor 1 andevaporates, the oil pressure increases, the regulator 13 opens thecontroller 11, and the oil continues to return to the compressor 1. Thissystem provides an uninterrupted safe operation of the compressor. Whilethis invention has been illustrated and described in accordance with thepreferred embodiments, it is recognized that variations and changes maybe made therein without departing from the invention as set forth in theclaims.

We claim;
 1. A method of controlling the compressor oil pressure in theunit consisting of a connected series, a compressor, a condenser, anevaporator, a suction accumulator with an inlet connected to saidevaporator with a line and two outlets. One of the outlets is connectedto said compressor with a suction line and another is connected to saidcompressor by a return line. A controller is placed on the return lineand a regulator with a set-point adjustment is connected to saidcompressor electrically. The said controller is designed to: feedrefrigerant vapor into the compressor; compress the refrigerant vapor;transform the vapor into a liquid; boil liquid refrigerant in theevaporator; separate refrigerant vapor from the mixture with oil andliquid refrigerant; feed vapor refrigerant to the compressor; feed theoil-liquid refrigerant mixture to the compressor; monitor oil pressurein the compressor; compare the value of the oil pressure to anestablished target value; prevent the entrance of oil-liquid refrigerantmixture into the compressor if the value of the oil pressure in thecompressor corresponds to a value installed on a set-point adjustment,allow the entrance of oil-liquid refrigerant into the compressor if theoil pressure in the compressor is more than the value installed on theset-point adjustment.
 2. A method of controlling the compressor oilpressure in the unit consisting of a connected series, a compressor, acondenser, an evaporator, connected to said compressor by a suctionline, a controller placed on the suction line, and a regulator with aset-point adjustment connected to said compressor electrically. Thecontroller is designed to: feed refrigerant vapor into the compressor;transform vapor into liquid; boil liquid refrigerant in the evaporator;feed vapor refrigerant to the compressor; monitor oil pressure in thecompressor; compare the value of oil pressure to an established targetvalue; prevent the entrance of oil-refrigerant vapor mixture into thecompressor if the value of the oil pressure in the compressorcorresponds to a value installed on a set-point adjustment; allow theentrance of oil-refrigerant vapor into the compressor if the oilpressure in the compressor is more than the value installed on aset-point adjustment.
 3. A unit consisting of a connected series of acompressor, a condenser, an evaporator, a suction accumulator with aninlet connected by a line to said evaporator, and two outlets. One ofthe outlets is connected to said compressor with a suction line andanother is connected to said compressor by a return line. A controlleris placed on the return line and a regulator with a set-point adjusteris connected to said compressor and electrically to said controller. 4.A unit consisting of a connected series of a compressor, a condenser, anevaporator connected to said compressor with a suction line, acontroller placed on the suction line and a regulator with a set-pointadjuster connected to said compressor and electrically connected to saidcontroller.
 5. A unit consisting of a connected series of a compressor,a condenser, an evaporator connected to said compressor with a suctionline, a controller placed on the line connecting said condenser withsaid evaporator, and a regulator with a set-point adjuster connected tosaid compressor and electrically connected to said controller.